The type placeholder _ was used in an item's signature, such as a function return type or static declaration, where an explicit type is required. The _ placeholder is only valid in local variable bindings where the type can be inferred.
E0121
rust The type placeholder _ was used in an item's signature, such as a function return type or static declaration, where an explicit type is required. The _ placeholder is only valid in local variable bindings where the type can be inferred.